1. Field of the Invention
This invention relates to asphalt compositions for use in the manufacture of pavement materials for paving traffic roads, walkways, air-port runways park lots and the like.
2. Prior Art
Conventional pavements chiefly comprised of straight asphalt have been often found defective when applied to roads susceptible to deformation or damage by heavy weight traffic, or under cold or snowy environmental conditions where tire chains or spiked tires are used. Typical solutions to this problem have been to admix an asphalt matrix with reformers such as natural rubber, SBR, butadiene rubber, isoprene rubber, or thermoplastic elastomers such as block copolymers of styrene-butadiene-styrene, styrene-isoprene-styrene and the like. Such reforming agents are known for their ability to reduce asphalt's thermal response, fluid deformation and frictional wear of asphalt-paved roads as well as to improve other asphalt characteristics including adhesion with aggregates and flexibility at low temperature.
There are currently used asphalt pavements containing certain open graded asphalt mixtures conducive to water penetration and drainage with a view to providing increased resistance to road slip and preventing water splash and a so-called "hydroplaning". Such pavements comprised of straight asphalt alone would be insufficient in compressive strength and water resistance, but these physical properties could be improved with use of the aforesaid reformers as is well known to one skilled in the art.
Those asphalt compositions which incorporate reforming agents tend to have high temperature viscosity considerably increased as compared to straight asphalt. It is therefore necessary to choose a relatively high temperature level for mixing reformed asphalt with aggregates in the preparation of a paving material. The working temperature at the site of construction would also have to be increased for roll-flattening the paved road surface to an extent to make the paving operation tedious and time-consuming.
So much more reformers would be required to achieve a target compressive strength of pavement for roads frequented by heavy traffic of large vehicles, or where water permeation is an important parameter. The use of increased amounts of reformers would lead to increased high temperature viscosity of reformed asphalt and hence aggravated paving operation.